The general purpose of this proposal is to determine whether microtubules (MT's) and microfilaments (MF's) have roles in the synthesis and secretion of lactose by the lactating mammary gland. This possibility is suggested by observations that drugs which disrupt MT's and MF's also inhibit secretion and synthesis, respectively. The following work is planned for the next grant year: (1) Complete studies on adapting the floating collagen gel technique to guinea pig mammary gland, including light and electron microscopic and lactose production studies following hormone-induced lactogenesis; (2) utilize the floating collagen gel cultures to follow changes in free, polymerized (MT), and total tubulin during induced lactogenesis; (3) utilize the improved 3H-cholchicine binding assay to measure tubulin pools in alveolar cells isolated from lactating and pregnant guinea pig mammary glands; and (4) carry out further studies on the effects of drugs, especially cytochalasin B, on MF's in mammary gland alveolar cells.